The first exanination an officer will do when he stops someone for DUI in the HGN test, AKA “pen test”. The test is a three step process and how you do will determine whether you ride home in your car or a cop car. Here are the 3 steps:
1. Smooth Pursuit
The first exam is called smooth pursuit. This is performed by moving an object, usually a pen, from a point near the defendant’s nose outward toward the side of the defendant’s face. This movement should take approximately 2 seconds. The defendant is asked to follow the movement of the pen with his eyes and to do so without moving his head. The officer starts with the left eye and observes whether the eye moves smoothly or with a jerking motion. A “normal” eye will move smoothly in a manner similar to a marble moving over a hard surface. If the defendant is under the influence of alcohol and/or certain drugs, nystagmus may be observed. Nystagmus refers to a jerking motion which is similar to rolling a marble over sandpaper. The eye does not proceed smoothly, but moves with a jerking motion. The test is then repeated on the right eye.

2. Maximum Deviation
The second part of the horizontal gaze nystagmus test is called maximum deviation. In this part of the test, the defendant is asked to follow the stimulus which is moved to the side of his face. The defendant’s left pupil is directed to the corner of the eye and the stimulus is held stationary for a minimum of 4 seconds. While the eye is in this position, it is observed for nystagmus. This process is repeated with the right eye.

3. Angle of Onset
The third part of the horizontal gaze nystagmus test is called angle of onset. This is to determine at what angle with the nose the eye commences to jerk. The exam is performed by placing the pen approximately 12-15 inches from the defendant’s nose and slowly moving it (approximately 4 seconds) toward the outer corner of his eye. The officer starts with the left eye and watches it closely for the first sign of jerking. If he observes any jerking, the officer stops moving the pen and holds it steady. The officer makes sure that the eye is jerking. If it is not, the officer is required to start the procedure over again by moving the pen further towards the outer portion of the eye and looking for the onset of jerking. Once the officer determines the point of onset, he estimates the angle.

Matthew Ruff is a DUI Attorney practicing is Torrance California.